1. Field
The present invention relates generally to a servo writer and a method for manufacturing a magnetic tape with a servo signal written thereon.
2. Description of Related Art
The magnetic tape on which digital data are recordable along its data tracks designed to have as narrow widths as possible to increase its recording density is provided with a servo signal written thereon in advance for use in the tracking control over a magnetic head so that the magnetic head can follow the narrow tracks. The servo signal is written on the magnetic tape by an apparatus called servo writer when the magnetic tape is manufactured in the factory (see U.S. Pat. No. 7,623,310 B2 corresponding to JP 2005-327386 A).
The servo signal serves to provide a reference to be used to locate the track positions on the magnetic tape, and thus should be written precisely in position (substantially without meandering or deviation in a tape width direction) along the length of the magnetic tape. In the magnetic tape drive, during recording or retrieving data, the magnetic head reads the servo signal to detect an amount of deviation of a track currently to be scanned for recording or retrieving the data with respect to the position of the magnetic head, and the magnetic head is moved to follow the tracks based on the detected amount of deviation; however, if the servo signal written in advance on the magnetic tape had already deviated too much in the tape width direction, the magnetic head would be unable to follow the tracks, whereby a tracking error would occur.
In order to write a servo signal precisely along the length of the magnetic tape, the servo writer typically uses a high-precision magnetic transport device which allows only a moderate amount of oscillation (deviation) of the magnetic tape in the tape width direction, and writes the servo signal on the magnetic tape by a fixed servo write head. As is generally known, it is important to figure out how to guide a magnetic tape at positions near a servo write head in order to minimize the lateral movement (oscillation) of the magnetic tape near the servo write head. To achieve this, a tape guide having a fixed cylindrical surface partially utilized as a tape guide surface may be adopted as disclosed in U.S. Pat. No. 7,623,310 B2 and JP 2007-287238 A, instead of a roller type tape guide (guide roller). In this case where a fixed cylindrical surface is partially utilized as a tape guide surface, a position error signal or PES (an indicator of the oscillation or deviation of a magnetic tape in the tape width direction) was evaluated to fall within a range of 150 to 250 nm.